The effect of wave characteristics on rivulet formation in heated liquid films

Formation of rivulets on the surface of non-isothermal water film falling vertically over the heaters with different sizes and boundary conditions was studied experimentally. The distances between rivulets were measured depending on Reynolds number, heat flux density and film path (a distance between the lower edge of a film-former nozzle and the measurement point of film flow characteristics). The breakdown of solitary waves at liquid film heating was revealed. Four zones of film path influence on rivulet formation were distinguished.     

Effect of viscosity on thermocapillary breakdown of a falling liquid film

Thermocapillary breakdown of a liquid film flowing due to gravity over a vertical plate with a heater of 150×150 mm is studied in a wide range of liquid properties (in particular, dynamic viscosity at the initial temperature varies from 0.91·10^-3 to 16.9·10^-3 Pa·s) and film Reynolds number (Re = 0.15-53.5). It is found that liquid viscosity has a significant effect on the threshold heat flux corresponding to film breakdown. To take into account the effect of liquid properties, the breakdown criterion traditionally used in literature was modified. This allowed successful generalization of all data obtained.     

Synchrotron infrared reflectance microspectroscopy study of film formation and breakdown on copper

This work demonstrates the utility of synchrotron infrared reflectance microspectroscopy in the far‐ and mid‐IR for the determination of the composition of electrogenerated surface films formed during the general and localized corrosion of copper in alkaline and bicarbonate solutions. Back‐reflection geometry has been employed to identify the anodic film formed on copper in 0.1 M NaOH solution at 0.3 V (versus a Ag/AgCl reference) to be mainly CuO. In 0.01 M NaHCO₃ solution general corrosion occurs with passive film formation below 0.2 V. The surface film at 0.2 V consisted mainly of bicarbonate, copper carbonate dihydroxide or malachite [CuCO₃·Cu(OH)₂], Cu(OH)₂ and possibly some CuO. At higher potentials the passive film breaks down and localized corrosion occurs leading to the formation of pits. The composition of the surface films inside the pits formed at 0.6 V was found to be essentially the same as that outside but the relative amount of Cu(OH)₂ appears to be higher.     

Influence of the ambient pressure on thin plate and film bending

The distributed lateral load on a plate located in a gas medium has been determined. The difference in the gas pressures of the plate surfaces results in a pressure drop and a lateral force, which depends on the middle surface curvature. It is shown that both these components of the lateral force must be taken into account in the general case. The influence of the second load component is small at a small ratio of the average pressure to the elastic modulus of the plate material and at a large relative thickness of the plate. At a small relative plate thickness and a large ratio of the average pressure of the medium to the elastic modulus of the plate material, the influence of the second component of the lateral load on the bending becomes significant. Cases of both linear and nonlinear plate bending are considered.     

金属表面镀高分子膜对真空击穿阈值的影响

探索提高金属表面真空击穿阈值的方法,对脉冲功率技术的发展和应用具有重要意义。在金属表面电子发射理论分析的基础上,采用有限元法计算阴极杆表面电场随二极管电压的变化规律,设计了实验系统,并开展了实验研究。实验对比了在脉宽约30 ns、阴极杆与阳极筒间隙12 mm时,钛合金TC4阴极杆在不同种类高分子膜（膜厚30～60 μm）下真空击穿阈值的变化情况。在表面粗糙度R_z（轮廓最大高度）为0.8 μm的TC4阴极杆表面分别镀环氧树脂膜和丙烯酸膜,实验结果表明,镀丙烯酸膜阴极杆的击穿阈值约505 kV/cm,相对于不镀膜阴极杆,击穿场强提高了约20.6%;在表面粗糙度R_z为0.2 μm的TC4阴极杆表面分别镀聚酰亚胺膜和聚醚醚酮膜,实验结果表明,镀聚酰亚胺膜阴极杆的击穿阈值为584 kV/cm,相对于不镀膜阴极杆,击穿场强提高了约28.1%。因此,在金属表面镀丙烯酸膜、聚酰亚胺膜可以有效提高金属表面的真空击穿阈值。     

Influence of Marangoni instability on evaporation of the polar liquid film

A thin film of an evaporating polar liquid on a solid substrate is investigated within the framework of the lubrication theory. Using linear analysis, we have found that stability of the film depends only on two control parameters: the evaporation and Maranagoni numbers. We demonstrate that the Marangoni effect plays a destabilizing role while evaporation stabilizes the film.     

About the effect of microtexture on liquid film formation on a vertical surface

Formation of a liquid film on the surface of a cylinder with microtexture was studied visually. The effect of microtexture on evolution of waves on the surface of viscous liquid falling over the outer surface of a vertical cylinder under the action of gravity depending on Reynolds number is shown. The phenomenon of microwave formation on the film surface was determined; the size of these waves is comparable with the microtexture pitch.     

Modeling of wave regimes on the film of viscous liquid falling down a vertical plate

Evolution of disturbances on the surface of liquid film falling free over a vertical plane is considered. In the case of low Reynolds numbers, the problem is reduced to investigation of a single equation describing evolution of film thickness disturbances. With the use of information about the structure of the family of steady-state traveling solutions to this equation, the typical scenarios of evolution for periodic disturbances were identified.     

Influence of thermocapillary effects on wave characteristics of the heated liquid film

Wave characteristics of the water film flow over a vertical plate with a heater were studied. Without a heat flux, data obtained perfectly coincide with results of other authors obtained for an isothermal liquid film. When heating the falling liquid, thermocapillary forces form the rivulets and thin film between them. It was found out that an increase in the heat flux causes a rise of the phase velocity and decreases the frequency of 3D waves. It is shown that in contrast to the known data for an isothermal liquid film, the average relative wave amplitude increases with a rise of dimensionless complex Re_loc/Ka _loc ^1/11 at relatively high heat flux densities in the interrivulet. The growth of wave amplitude under the action of thermocapillary forces was revealed in the interrivulet, what corresponds to calculations. The work was financially supported by the Russian Foundation for Basic Research (Grants Nos. 05-08-33325-a and 06-01-00360-a), Federal Target R&D Program (State contracts Nos. 02.438.11.7002 and NSh-6749.2006.8), and SB RAS (International interdisciplinary project No. 111).     

倾斜波动壁面上液膜表面波演化特性的影响

对倾斜波动壁面上流体表面波的演化规律进行了研究. 考虑壁面形状为正弦波动壁面的情况, 分析液膜流动的线性稳定性, 并研究不同倾斜角度下扰动波波形随时间的演化情况及流经不同壁面形状时扰动波的波形变化. 对整体的波形结构分析可知, 随着时间的演化, 扰动波的演化过程呈现为更大波长的近周期变化规律, 与平板上的流动结构对比发现波动情况变得更加复杂; 当液膜流经波动壁面时, 扰动波在空间上不再呈现规律性变化, 且随着壁面倾斜角度的增加, 扰动波的振幅逐渐增加; 在相同的壁面倾角下, 波动壁面上的扰动波振幅大于平板壁面的扰动情况, 且波形扭曲程度更明显; 随着Re的增加, 扰动波振幅逐渐增加, 其对应波形的扭曲程度加深, 且随着壁面振幅的增加, 静态波振幅及扰动波振幅均随之增加, 对应的行进波周期不变. 最后, 分析了壁面倾斜角度对流动稳定性的影响.     

Determination of the chain inclination angle of isothermally crystallized bulk polyethylene

The crystal lamella is well established as a basic structural unit of most semicrystalline polymers. It is also accepted that the chain axis is generally not parallel to the normal to the large flat lamella surfaces, but inclined at some angle θ to it. Due to the random orientation of lamellae in bulk polymers where spherulitic growth predominates, no direct method exists for determining θ. However, the angle has been determined by acid etching bulk samples and then using electron microscopy techniques on fragments. An alternative approach is utilized in this work. The etched fragments, after suitable washing procedures, were sedimented to form an oriented mat. An x-ray diffraction technique was employed in which the regions of high pole density for several crystallographic planes were determined. From these results, the inclination angle was determined to be 40.4°, with a standard deviation of 1.5°. This study represents the first time that an x-ray pole figure technique has been used to determine chain inclination in isotherm-ally crystallized PE.     

Reynolds number invariance of the structure inclination angle in wall turbulence

Cross correlations of the fluctuating wall-shear stress and the streamwise velocity in the logarithmic region of turbulent boundary layers are reported over 3 orders of magnitude change in Reynolds number. These results are obtained using hot-film and hot-wire anemometry in a wind tunnel facility, and sonic anemometers and a purpose-built wall-shear stress sensor in the near-neutral atmospheric surface layer on the salt flats of Utah's western desert. The direct measurement of fluctuating wall-shear stress in the atmospheric surface layer has not been available before. Structure inclination angles are inferred from the cross correlation results and are found to be invariant over the large range of Reynolds number. The findings justify the prior use of low Reynolds number experiments for obtaining structure angles for near-wall models in the large-eddy simulation of atmospheric surface layer flows.     

Spontaneous breakdown of the gauge chiral symmetry and the cabibbo angle

From the general treatment of the spontaneous breakdown of the chiral SU(3)xSU(3) group down to the electromagnetic U(l) gauge group it is conjectured that the bare Cabibbo angle isπ/4. Imposing the self-consistency condition of Cabibbo and Maiani on the weak and electromagnetic corrections to the chiral symmetry breaking Hamiltonianh=ε₀ u ₀+ +ε₃ u ₃+ε₈ u ₈ leads to the determination of the physical Cabibbo angle. The agreement with the experimental value is reached when the parametrization ofh of Brandt and Preparata is used.     

平衡接触角对受热液滴在水平壁面上铺展特性的影响

壁面温度是影响壁面润湿性的重要外部条件. 为解决液滴铺展中三相接触线处应力集中问题, 已有研究多采用预置液膜假设, 但无法探究壁面温度对润湿性的影响. 本文针对受热液滴在固体壁面上的铺展过程, 基于润滑理论建立了演化模型, 通过数值模拟, 从平衡接触角角度分析了温度影响壁面润湿性及铺展过程的内部机理. 研究表明: 随温度梯度增大, 液滴所受Marangoni效应增强, 致使液滴向低温区的铺展速率加快; 铺展过程中, 位于高温区的接触线与液滴主体部分间形成一层薄液膜, 重力与热毛细力先后主导该区域的铺展; 当液-固或气-液界面张力对温度的敏感度高于另两个界面时, 低温区方向的平衡接触角不断增大, 使壁面润湿性恶化, 导致液滴铺展减慢; 而当气-固界面张力对温度的敏感度高于其他两个界面时, 低温区方向上的平衡接触角将减小, 由此改善壁面润湿性, 加快液滴铺展; 在温度影响壁面润湿性和液滴铺展过程中, 平衡接触角起关键作用.     

Femtosecond laser-induced breakdown of multilayers and gold film

We report single-shot damage threshold as a function of pulse duration (50 - 900 fs) for MgF2/ZnS 800-nm omnidirectional-reflection film, interference filter, and gold film. The results indicate that the damage with ultrashort pulse is nonthermal, which is different from that with long pulse. Additionally,the ablation crater depths of 45° high-reflection film and interference filter are presented. A logarithmic relation between the ablation depth and pulse fluence, which is similar to that of transparent materials, is found.     

颗粒孔洞流的最大休止倾角和流量公式

实验测量了重力驱动下的玻璃珠颗粒样品通过不同倾角和孔径的圆形孔洞的卸载流量.发现无论孔径大小,流量均与倾角的余弦呈良好的线性关系;线性外推得到的零流量角,即流量休止临界角随颗粒粒径与孔洞直径之比的减小而线性增加;在无穷大孔径极限下,此临界角在Bagnold角的误差范围内与样品的安息角一致.这些结果表明流量随倾角余弦线性变化的经验公式能揭示临界角的行为和特性,这是参数随倾角变化的Beverloo公式所不能描述的. 关键词： 颗粒物质 倾斜孔洞流 Beverloo公式     

一种新式单倾角高温超导磁悬浮车永磁道岔设计

高温超导(HTS)磁悬浮列车是下一代新型磁悬浮交通工具的备选方案之一。非接触轮轨系统使得轨道道岔面临诸多问题。给出了一种单倾角永磁体结构的新型机械永磁道岔结构。在使用单倾角永磁体装配永磁道岔时,两相邻永磁体之间的楔形缝隙用于调整永磁轨道在水平面上的曲率,以适应磁悬浮车变道目的。成功推导出了单倾角永磁体的几何尺寸、倾角大小和永磁道岔最小转弯半径之间的关系数学表达式并通过仿真计算进行了初步验证。计算结果表明,当永磁道岔换轨时,这种微小的差别不足于影响高温超导磁悬浮车的运行稳定性。     

Large-Biot-number non-isothermal flow of a thin film on a stationary or rotating cylinder

Using the lubrication approximation we investigate two-dimensional steady flow of a thin film of fluid with temperature-dependent viscosity on a uniformly heated or cooled horizontal cylinder, which may be stationary or rotating about its axis, in the case when the Biot number (a measure of heat transfer at the free surface) is large.We show that the film thickness (but not the fluid velocity) may be obtained from that in the isothermal case by a simple re-scaling.     

Influence of film morphology on thin film ferromagnetism

Cobalt, nickel and their alloy, Co₁Ni₉, films were epitaxially grown on Cu(100) under different growth conditions and subsequent treatments and studied using surface magneto-optic Kerr effect (SMOKE) in an attempt to understand the effects of film morphology on the magnetic properties. CO contamination can significantly reduce the magnetization and Curie temperature. Thermal desorption spectroscopy (TDS) shows that CO desorbs at 422 K from Ni and 410 K from Co₁Ni₉ at a heating rate of 6 K per minute. Annealing the films below 450 K produces smooth and clean films with stable magnetic behavior. However, annealing at higher temperatures results in Cu segregation and island formation leading to the finite-size ferromagnetic or even superparamagnetic behavior.